Numerous types of solar collectors have been designed to not only optimize the capture of solar radiation but to do so in an efficient and reliable manner with units that are aesthetically attractive. Most solar collector units consist of a large collector plate across which a fluid transfer medium such as water or air is passed. The heat from the collector plate is transferred to the fluid and the heater fluid can either be used immediately or passed into a storage chamber remote from the collector unit. The heated fluid is stored in the chamber until it is needed to heat a building structure or the like. The collector plates are typically covered with large expanses of glass or other transparent material which will allow solar radiation to pass therethrough and be absorbed by the solar collector plate.
Numerous systems have been employed for optimizing the transfer of solar radiation to the heat transfer medium and these different systems have met with varying degrees of success. More recently, it has become desirable to design the solar collector units so that they can be interconnected to cooperate in capturing solar radiation and transferring the heat to a fluid which can be stored in a storage area for later use.
Solar energy collecting systems with a plurality of individual solar collecting units encounter problems with expansion and contraction of the individual units. Such units undergo radical temperature fluctuations when in use and between uses. Past units have particular problems in passing the fluid through the units in a manner which will optimize the heat transfer from the units to the fluid and minimize or eliminate fluid losses during the expansions and contractions of the unit. U.S. Pat. No. 3,961,619 to Estes et al. issued on June 8, 1976, illustrates an arrangement of solar units designed to accommodate lateral movement between the units. Estes' units are individually supported on a horizontal surface by angle members 44 and 46 and are joined by bellows 104 and 112 extending between the units. These bellows are difficult to work with and adjacent units cannot be easily and quickly connected together. It appears that Estes' bellows 104 must be welded at each end to a solar unit. A simplistic male-female coupling is illustrated in U.S. Pat. No. 3,996,911 issued to Quick on Dec. 14, 1976; however, Quick's rectangular couplings are not designed to accommodate expansion and contraction as he states in lines 57-58 of his column 3 that the units abut each other so that the warmed air is not allowed to cool between units. More sophisticated couplings are illustrated in FIGS. 5-8 of U.S. Pat. No. 3,976,508 to Mlavsky issued on Aug. 24, 1976. The male-female couplings shown in Mlavsky's FIGS. 6-8 all have a portion of the male and female members soldered or otherwise bonded to each other so that the units can neither be quickly and easily assembled nor replaced if needed (see lines 8-11, 24-25, and 57-59 of his column 10).
Problems have also been encountered in designing a system including a plurality of solar collecting units such that the units can be mounted on a supporting surface in a quick and easy manner. This problem is especially acute if the supporting surface is a roof or other inclined surface. Two methods of mounting units side-by-side are illustrated by U.S. Pat. No. 3,174,915 to Edlin issued on Mar. 23, 1965 and U.S. Pat. No. 3,980,071 issued to Barber on Sept. 14, 1976. Each of these methods involves the use of an elaborate set of railings that are difficult and awkward to work with. The railings also appear to protrude upwardly from the support surface a distance such that they would block some sunlight when the sun is at low angles. The system of Barber would appear to require considerable time and labor at the construction site to install the railings.
Prior art solar collectors utilizing water as a heat transfer medium have been plagued with corrosion problems so that it has become desirable to utilize a non-corrosive material, such as stainless steel, in the manufacture of the collector plates. Certain characteristics of stainless steel, however, such as its ability to be deformed, have prevented others in the art from being able to use stainless steel. Another important feature of an efficient collector is the cross-sectional shape of its channels. Many collectors have channels with circular cross sections as illustrated by U.S. Pat. No. 3,999,536 to Bauer et al. issued on Dec. 28, 1976. Others have hexagonal cross sections such as U.S. Pat. No. 3,961,619 to Estes et al. issued on June 8, 1976. Still others have semi or half hexagonal cross sections like U.S. Pat. No. 3,399,664 to Suhay issued on Sept. 3, 1968 and semi-circular like U.S. Pat. No. 3,190,816 issued to Adamec on June 22, 1965. The channels of Suhay and Adamec each have an upper, flat side. Channels with circular cross sections tend to establish a rather large boundary layer that acts as an insulator and inhibits the flow of heat from the collector into the fluid. Channels having hexagonal cross sections with a larger surface area to volume ratio than circular are preferred. Hexagonal cross sections are also preferred over circular because they tend to set up less of a heat insulating boundary layer. In one embodiment, the present invention discloses channels with substantially rectangular cross sections. Although the theory is not fully understood, these rectangular channels have been found to have thinner boundary layers and higher threshhold rates for turbulent flow than other channel designs.
The ideal collector unit would be simple in design, able to safely use tap water, easily and completely drainable, attractive, durable, efficient and easily and quickly installable. The unit would also be lightweight and require little or no structural changes to the building on which is to be placed. Further, the unit would be able to be arranged with other units into a tight pattern on the support surface so that a very high percentage of the total light striking the support surface is received by the units. Each unit would also be completely assembled upon arrival at the building and would have an arrangement for easily and quickly replacing any unit in the pattern of units that has become damaged by accident or vandalism. The present invention offers such a collector unit and an arrangement for mounting a plurality of the units on a supporting surface to form an efficient system.